In the majority of applications printing proceeds by pressure contact of an ink-laden printing form with an ink-receiving material which is usually plain paper. The most frequently used impact printing technique is known as lithographic printing based on the selective acceptance of oleophilic ink on a suitable receptor.
In recent times however so-called non-impact printing systems have replaced classical pressure-contact printing to some extent for specific applications. A survey is given e.g. in the book “Principles of Non Impact Printing” by Jerome L. Johnson (1986), Palatino Press, Irvine, Calif. 92715, USA.
Among non-impact printing techniques ink jet printing has become a popular technique because of its simplicity, convenience and low cost. Especially in those instances where a limited edition of the printed matter is needed ink jet printing has become a technology of choice. A recent survey on progress and trends in ink jet printing technology is given by Hue P. Le in Journal of Imaging Science and Technology Vol. 42 (1), January/February 1998.
In ink jet printing tiny drops of ink fluid are projected directly onto an ink receptor surface without physical contact between the printing device and the receptor. The printing device stores the printing data electronically and controls a mechanism for ejecting the drops image-wise. Printing is accomplished by moving the print head across the paper or vice versa. Early patents on ink jet printers include U.S. Pat. No. 3,739,393, U.S. Pat. No. 3,805,273 and U.S. Pat. No. 3,891,121.
The jetting of the ink droplets can be performed in several different ways. In a first type of process a continuous droplet stream is created by applying a pressure wave pattern. This process is known as continuous ink jet printing. In a first embodiment the droplet stream is divided into droplets that are electrostatically charged, deflected and recollected, and into droplets that remain uncharged, continue their way undeflected, and form the image. Alternatively, the charged deflected stream forms the image and the uncharged undeflected jet is recollected. In this variant of continuous ink jet printing several jets are deflected to a different degree and thus record the image (multideflection system).
According to a second process the ink droplets can be created “on demand” (“DOD” or “drop on demand” method) whereby the printing device ejects the droplets only when they are used in imaging on a receiver thereby avoiding the complexity of drop charging, deflection hardware, and ink recollection. In drop-on-demand the ink droplet can be formed by means of a pressure wave created by a mechanical motion of a piezoelectric transducer (so-called “piezo method”), or by means of discrete thermal pushes (so-called “bubble jet” method, or “thermal jet” method).
Ink compositions for ink jet typically include following ingredients: dyes or pigments, water and/or organic solvents, humectants such as glycols, detergents, thickeners, polymeric binders, preservatives, etc. It will be readily understood that the optimal composition of such an ink is dependent on the ink jetting method used and on the nature of the substrate to be printed. The ink compositions can be roughly divided in:
water based; the drying mechanism involves absorption, penetration and evaporation;
oil based; the drying involves absorption and penetration;
solvent based; the drying mechanism involves primarely evaporation;
hot melt or phase change: the ink vehicle is liquid at the ejection temperature but solid at room temperature; drying is replaced by solidification;
UV-curable; drying is replaced by polymerization.
WO 01/020078 discloses a compound of any of formulas I to X, or IA to XA


U.S. Pat. No. 6,232,469 discloses 4-acylamino-2,2,6,6-tetramethyl-piperidine derivatives represented by formula (A′):
wherein R1 represents a hydrogen atom, a hydroxyl group, an oxyradical group, an aliphatic group, an acyl group, an aliphatic oxy group or an acyloxy group; and R2′ represents an alkyl group or an alkenyl group having 3 to 7 carbon atoms and 2 to 6 hydroxyl groups, said alkyl or alkenyl group being unsubstituted or substituted with an alkyl group. U.S. Pat. No. 6,232,469 further discloses an antioxidant composition for color diffusion transfer photographic materials or ink-jet dyes comprising the 4-acylamino-2,2,6,6-tetramethylpiperidine derivatives represented by formula (A):
wherein R1 represents a hydrogen atom, a hydroxyl group, an oxyradical group, an aliphatic group, an acyl group, an aliphatic oxy group or an acyloxy group; and R2 represents an alkyl group or an alkenyl group having 3 to 7 carbon atoms and 2 to 6 hydroxyl groups.
JP 61-146591 discloses an ink-jet recording medium that form a recording image using aqueous ink that contains a water-soluble dye, characterized in that the recording medium contains a hindered amine type compound, in particular a molecule represented by formula (I):
wherein R5 is a hydrogen atom or an alkyl group of C1 to C8, a benzyl group, an allyl group or an acetyl group and preferably a hydrogen atom or a methyl group; R1, R2, R3 and R4 are lower alkyl groups, carbonyl groups etc. and preferably methyl groups and/or ethyl groups. JP 61-146591 further discloses that if n=1, A is —NH2, —OH, ═CH2, ═O, —R, —OR, —OCO—R, —NHCH2CH2CH2OCH3, —NHCSSH, phenyl, —CH═CH2, (here R is an alkyl group),
etc.; and if n=2 A is —O—C(═O)—(CH2)m—C(═O)—O— (m is 1 to 14),
—NH(CH2)3NH—,

It is known that the ink-receiving layers in ink-jet recording elements must meet different stringent requirements:
the ink-receiving layer should have a high ink absorbing capacity, so that the dots will not flow out and will not be expanded more than is necessary to obtain a high optical density;
the ink-receiving layer should have a high ink absorbing speed (short ink drying time) so that the ink droplets will not feather if smeared immediately after applying;
the ink dots that are applied to the ink-receiving layer should be substantially round in shape and smooth at their peripheries. The dot diameter must be constant and accurately controlled;
the receiving layer must be readily wetted so that there is no “puddling”, i.e. coalescence of adjacent ink dots, and an earlier absorbed ink drop should not show any “bleeding”, i.e. overlap with neighbouring or later placed dots;
transparent ink-jet recording elements must have a low haze-value and be excellent in transmittance properties;
after being printed the image must have a good resistance regarding water-fastness, light-fastness, and good endurance under severe conditions of temperature and humidity;
the ink jet recording element may not show any curl or sticky behaviour if stacked before or after being printed;
the ink jet recording element must be able to move smoothly through different types of printers;
All these properties are often in a relation of trade-off. It is difficult to satisfy them all at the same time.
A particular problem is the stability of the color densities of the finished color ink jet image when exposed to light for a longer period (“light-fastness”). As well-known by those skilled in the art, the light fading of colorants is mainly due to an oxidative decomposition of the colorant catalyzed by light, in particular by the UV spectral part. Therefore, there is a permanent need of more effective compounds, which stabilize the colorants of the ink jet image against fading by light.